Circuit interrupter



, 1942. H. 1.. RAWLINS ETAL Dec. 1

C IRCUIT INTERRUPTER Filed May 31, 1940 jnsu/af/bn |NVENTOR3 Herbs/f A,EON/ff)! m0 Ill H 7 have: 07. h/a// ace v Patented Dec. 1, 1942' Icmoorr mrsnaurna Herbert L. Rawlins, Wilkinsburg, and James M.

Wallace, Braddock, Pm, assignors to Westinghouse Electric &Manufacturing Company,

East Pittsburgh, Pa., a corporation of Pennsylvania Application May 31,1940, Serial No. 338,116

(cl. zoo-as) 12 Claims.

Our invention relates generally to electric circuit interruptingapparatus, and more particularly to interrupting apparatus capable ofauto- .matically interrupting a circuit in response to the passagetherethrough of currents above a predetermined value, and which willoperate to automatically reclose the circuit a predetermined time afteran interrupting operation.

We have embodied our invention in a reclosing circuit breaker structurewhich is particularly adapted for relatively low voltage distributionwork, 15 kilovolts and under, although it should be understood thatcertain principles of our inventionmay be used with interrupters ofhigher voltage ratings.

One object of our invention is to provide a novel circuit breaker whichis operable to automatically reclose the circuit following aninterrupting operation, and which is compact in structural iorm, andeconomical to manufacture.

Repeating fuse structures are often employed in the protection ofcircuits subjected to rapidly clearing faults to restore service Onthese lines after one fuse blows. Such constructions are quite complexand cumbersome and therefore expensive to manufacture. Furthermore, eachblown fuse in such structures must be-manually re-fused.

Our improved circuit breaker construction is designed in one applicationthereof to replace re- .peating fuse constructions, and all thefunctions nectible from its associated circuit.

Another object of our invention'is to provide a novel construction of. asmall 011 circuit breaker with all of the parts thereof mountedcompactly in a single unitary container, arranged to automaticallyreclose the circuit following an interrupting operation. I

A further objectjof our invention is to provide in a circuit breakerconstruction of the type capable of automatically reclosing the circuitfollowing an interrupting operation. novel means for automaticallydetermining the number of successive reclosing operations.

Another object of our invention is to provide in a circuit breaker,novel latch means for maintaining the breaker contacts closed.

A still further object on our invention is to provide novel control andmotive means for a movable circuit breaker contact to effect automaticreclosure of said contact following a circuit interrupting operation.

These and other objects of our invention will become more apparent uponconsideration oi the following specification of a preferred embodimentthereof, taken in connection with the attached drawing, in which:

Figure l is a longitudinal sectional view of a circuit interrupterconstructed in accordance with our invention and illustrating a breakcontact with which the interrupter may be associated;

Fig. 2 is a view of our novel interrupter similar to that shown in Fig.1, but with the contacts thereof shown in a closed position, and with ahinge contact mounting for the device also shown;

Fig. 3 is a partial transverse sectional view taken substantially on theline III- H of Fig. 2 and looking in the direction of the arrows; and

Fig. 4 is an enlarged partial longitudinal sectional view showing thebimetal control means.

Referring to the drawing, we have shown our interrupter as beingenclosed in a substantially cylindrical insulating casing 2 which may beof any desired insulating material, such, for example, as iiber,porcelain or glass. The casing 2 is provided with, end terminal caps 4and 8 for closing the opposite ends thereof and forming terminals forthe interrupter. The terminal cap 4 is provided with an integralperipheral flange adapted to telescope over the reduced end of casing 2and be secured thereto, for example, as by the'screws I. The terminalcap 4 is also provided with an integral hookeye extension 5 for thereception of a hook stick or other operating member for a purpose to behereinafter further described.

The terminal cap 6 at the opposite end of the casing 2 is provided withan interiorly threaded flange adapted to be threadedly engaged with'theouter surface oi the adjacent reduced outer end of the casing 2. Theterminal caps 4 and 6 are provided with outwardly projectingsubstantially centrally positioned terminaltongues l0 and II,respectively. The terminal tongue I 2 is adapted to be received betweenthe sides of a split hinge contact I! so as to be pivotally mountedtherebetween on a pivot bolt I! which passes through aligned aperturesin the sides of the terminal contact H and hinge tongue l2. The otherterminal tongue 10 which may be termed a break terminal tongue isadapted to be received between the sides of a split break contact II,the sides of which are connected by a spread-preventing bolt 0, toprevent undue spreading of the sides of the split contact IS. The breakterminal tongue II is provided with a notch 22 opening on the side ofthe tongue adjacent the break contact I! for receiving the bolt in theclosed position of the interrupter. provided with resilient cup-shapedwashers 24 at each side thereof for limiting the pressures which may beexerted by the bolt and for providing some resiliency for relativeoutward movement of the sides of the split contacts.

Each of the contacts I4 and it are provided with integral laterallyextending terminal portions to which line conductors may be secured,respectively, and each contact is suitably secured to supportinginsulators 28 which may be, in turn, mounted in any desired manner on asupport.

It is believed obvious that the structure thus far described is that ofa disconnecting type of circuit interrupter similar to a disconnectingswitch, and that the circuit may be interrupted to provide a relativelylarge air gap in the circuit by merely exerting a pull on the hook-eye Bto rotate the interrupter about pivot bolt IQ for movement of its breal:terminal tongue [0,

into or out of engagement with respect to the break contact II. Thus, inaddition to the various functions which will be hereinafter set forth,it is obvious that our novel interrupter is' capable of performing .thefunction of a disconnect ing switch as respects interrupting the circuitto provide a large air gap therein.

On the inner surface of the interrupter terminal cap 6 we secure asupporting plate 20 such, for example, as by welding or the like, whichhas its exposed surface notched to receive a plurality. of resilientcontact supporting strips 22, the inner ends of which are received inthe above mentioned notches and secured therein, such, for example, asby soldering or welding. Each contact strip 22 is provided at its outerend, either integral therewith or fixedly attached thereto, withlaterally projecting contact button portions 24. The outer ends of theresilient contact strips 22 and the contact buttons 84 are electricallyconnected to the supporting base 2| by flexible shunts 38 of a goodconducting material such as, i'or example, copper or the like.

A slidably mounted contact rod 28 is provided to cooperate with thecontact buttons 24, and as shown is substantially centrally mounted withrespect to the insulating casing 2, and slidable substantiallylongitudinally of the casing. The contact rod 28, as shown, is made upof three sections with one end section 42 being of a conducting magneticmaterial, such, for example, as iron or the like. The section 42, asshown, has an interiorly threaded socket for receiving a reducedthreaded projection'on the intermediate section 42 which should be ofconducting -material which is substantially non-magnetic v wards themovable contact rod 38, we provide a centrally apertured insulatingbai'ile member 52, which may be of any desired insulating material Thecontact bolts 20 and ii are preferably an insulating material which iscapable of evolving an arc extinguishing gas when in proximity to anelectric arc, such as fiber or the like. The bailie 52 is provided witha laterally extending integral sleeve portion 54, the outer surface ofwhich is threaded to engage the interior threads provided on the innersurface of the cylindrical casing 2. The central aperture through thebaille 52 is provided with annular grooves 56,

The closed circuit position of the contacts is shown in Fig. 2, and itwill be observed that when the contact rod 2| is moved upwardly to openthe circuit that an arc will be drawn between the contact buttons 24 andthe lower end of the conducting section 40 of the contact rod,

which are will be confined as the contact rod moves upwardly, betweenclosely spaced walls of insulating material defining the exteriorsurface of the insulating rod section 44 and the interior surface of theaperture in baffle 52. This will closely confine and compress the arcwhile exposing the same to the reservoirs of are extinguishing liquidpresent in the notches 45 and 56 of the insulating members 44 and 52, tothereby effectively extinguish the arc. This arc extinguishing structureis similar to that shown in the copending application of B. P. Baker,Serial No. 230,946, filed September 21, 1938, now Patent No. 2,253,009,issued August 19, 1941, and assigned to the assignee of thisapplication.

Somewhat above the middle of the insulating casing 2, we provide anannular insulating sup-' porting sleeve 50, the outer surface of whichis threaded to engage with the threaded interior surface or the casing2, and this supporting sleeve is provided at its upper end with anintegral laterally extending chordal segment 64 for supporting abimetallic control strip 82. The bimetal control strip 02 has one endthereof secured to the outer surface of the segment OI by a clampingplate 41 secured to the segment 60 as by screws II which pass throughthe clamping bar and bimetal 22 to find threaded engagement in thesegment 00. The screw II also serves to mechanically and electricallysecure a conducting strip 10 to the clamping plate and the upper end ofthe bimetal strip 62. The conducting'strip 10 extends from the upper endof the bimetal strip 82 to the inner wall of the casing 2 and along thiswall to be secured between the adjacent end of the casing and theterminal cap 4,

The bimetallic control strip 02 is constructed in a manner well known inthe art with two metallic laminations 84 and i0 suitably securedtogether as by welding or the like, and which laminations are ofmaterials having different coefiicients of expansion. In this particularinstance, it is desired to have the lower end of the bimetal deflect tothe left as seen in the draw- -ing. Therefore, the lamination I shouldbe of trol strip 82 in any desired manner such, for

example, as by soldering or the like.

As seen more particularly in Fig. 3, the lower end of the bimetal strip02 is provided with a .ing 2 and end terminal cap 8.

laterally projecting contact button I4, positioned at one side of thelongitudinal center of the bimetal strip 82, for cooperation with oneleg I8 of a generally U-shaped bracket member 18, the outer leg of whichis secured to the insulating supporting sleeve 58, for example, as bythe screw 88. The bracket 18 is adapted to be connected to one end of asolenoid coil 82 by a conductor 8!.

The solenoid coil 82 is suitably supported in a hollow annularinsulating support 84, the outer surface of which is threaded to bethreadedly engaged with the inner threaded surface of the casing 2. Theinsulating support 84 may be of any desired insulating materialpreferably a moldable or plastic material which may be formed about thesolenoid coil 82.

A conductor 88 is adapted to connect the other end of the solenoid coil82 to one terminal of a fusible element 88, the other terminal of whichis connected to a conducting strip 88 having one end angularly bent tobe clampingly received between the adjacent end of the insulating cas-It will be ob served that the fusible element 88 is provided with aninsulating sleeve 82 for a purpose to be hereinafter referred to.

Intermediate the insulating supports 88 and 84 we have provided anannular supporting member 84 which may be either ofmetal or insulatingmaterial, for supporting a latch member for maintaining the movablecontact in engagement with the fixed contact buttons 84. The supportingsleeve 84 like the other supporting sleeves, is exteriorly threaded tothreadedly engage with threads formed on the inner wall of the casing 2.

The supporting sleeve -84 is provided with a pivot supporting earforsupporting a pivot pin 88 on which is pivotally mounted a latch lever88. A coil biasing spring I88 has an intermediate portion thereof coiledabout the pivot pin 88, and has its end portions engaging with the latchlever 88 and supporting sleeve 84, respectively, for biasing the latchlever 88 in a counterclockwise direction as seen in Figs. 1 and 2. Theouter end of the latch lever 88 is turned laterally and notched as atI82 for latching engagement with the free end of the bimetal strip 82 asis clearly shown in Fig. 2.

The electrical circuit through our interrupter may now be traced fromthe upper contact terminal 28 through the break contact l8, breakterminal tongue l8, terminal cap 4, conductor I8 to the upper end of thebimetal strip 82. As shcwn'in Fig. 1, the circuit then proceeds from thebimetal strip 82, its contact button 14, U- shaped bracket 18, conductor8|, solenoid 82, conductor 88, fusible element 88, conducting'strip 88to the lower terminal cap 8, hinge terminal tongue l2, hinge contact l4and its terminal 28, y In this. position of the parts, the solenoid 82is energized so as to attract the magnetic portion 42 of the movingcontact rod 88 and move the lower end of the conducting section 48 ofthe contact rod quickly into engagement with the relatively fixedcontact buttons 84 against the bias of coil tension spring 48.

As isapparent from Figs. 1 and 2 of the drawing,the latch lever 88 isadapted to move into a lateral slot 88 through the outer end of themagnetic section 42 of the moving contact rod, so that when the rodmoves from the position shown in Fig. 1 to the position shown in Fig. 2,

the latch lever 88 is moved in a counterclockwise tact supporting plate88 to the lower terminal direction under the influence of its biasingspring I88, so that the outer curved end thereof engages the lowerportion of the bimetal strip 82. This engagement will take place beforethe limit of motion in a downward .direction of the contact rod 88 isreached and substantially at the same time or slightly thereafter thelower end of the conducting rod portion 48 engages contact buttons 84.Thereafter continued movement of these parts will enable the latch lever88 to exert a camming action on the bimetal strip 82 to move the lowerend of the same-towards the left as seen in Figs. 1 and 2 to therebydisengage the bimetal contact button 14 from the conducting bracket '18,thus interrupting the circuit to the solenoid 82 and permitting thelower end of the bimetal strip to become seated in the notch 182 at theextremity of the latch lever .88. This is the position shown in Fig. 2of the drawing. Engagement of rod portion. 48 with contact bu tons 84obviously short circuits the solenoid 82, and continued movement in thelocked position shown in Fig. 2 is due to the momentum of the cwointactrod 88 and associated parts moving there- In Fig. 2 of the drawing thecircuit through the solenoid is interrupted, and the circuit through theinterrupter now extends from the lower end of the bimetal strip 82 byway of flexible conductor I2, moving contact rod 88, relatively fixedcontact buttons 84, shunts 88, concap 8. This is the normal closedcircuit position of the interrupter. Upon the occurrence of an overloadon the circuit associated with the interrupter, above a predeterminedmagnitude, the

bimetallic strip 82 will become heated and the lower end thereof will bedeflected toward the left as seen in Figs. 1 and 2, for the reasonsdescribed above, so as to free the lower end of the strip 82 from thenotch in the latch lever 88. This will then permit the coil tensionspring 48 to quickly draw the contact rod 88 away from the relativelyfixed contact buttons 84 to the position shown in Fig. l.

The contacts will remain in an open position following such aninterrupting operation until the bimetal has had time to cool and moveback to the position shown in Fig. 1 where the contact button 14 thereofagain closes thesolenoid circuit, whereupon the contact 88 is moved intoand locked in engagement with the relatively fixed contact buttons 84 inthe manner described above.

If the overload has been cleared, the interrupter contacts will thenremain closed. However, if the overload is still present, the contactswill again be opened automatically in the manner described above, and,after a predetermined time depending upon the length of time requiredfor dissipating heat from the bimetallic strip '82, the contacts willagain be closed.

It is understood, of course, that our interrupter is designed to beoperated with the casing 2 substantially entirely filled with an arcextinguishing liquid such, for example, as an insulating oil with atleast the bimetal strip 82 conducting section 48 of contact rod 88,relatively fixed contacts 82, 84 and fusible element 88 being submergedbeneath the surface of the liquid. It can be readily appreciated that inaccordance with the description of the operation stated above that if apermanent overload or a short appears on the line with which ourinterrupter is associated that the interrupter contacts would circuithaving means for limiting the number keep on interrupting and reclosingthe circuit an indefinite number of times. Therefore, to avoid needlesswear on the moving parts of the interrupter, and especially in view ofthe fact that it has been found that all faults not of a permanentcharacter are usually cleared in a relatively few seconds, so thatapproximately 90% of self-clearing faults will be removed by the thirdsuccessive reclosure of the associated circuit, we will now proceed todescribe means for limiting the number of successive operations of ourinterrupter.

This is accomplished by the fusible element 88 connected in circuit withsolenoid 82 so as to be energized only during the relatively short timewhen the contact rod 38 is being moved by the solenoid 82 intoengagement with the fixed contact buttons 84. The fusible element 88 isconstructed so as to have low heat dissipating characteristics, and itis for this purpose that the insulating sleeve 82 is provided about thefusible element, that is, for inhibiting the dissipation of heat fromthe fusible element. Thus, on the first reclosure of our interrupter thefusible element 88 will be heated a certain degree, and if a secondreclosure immediately succeeds the first, the fusible element 88 willnot as yet have lost all of the heat generated thereby on the firstreclosure, and therefore will be heated to a higher temperature.Similarly, if a third reclosure immediately succeeds the second, thefusible element will be heated to a still higher temperature, such that,if the interrupter attempts to reclose on a fourth immediatelysuccessive interruption the fuse will be thereby heated to a high enoughtemperature to melt and thereby interrupt the solenoid circuit, so thatit will be ineffective to reclose the interrupter contacts.

When the fusible element 88 blows, the inter-- rupter then remains openand will require merely replacement of the fusible element to again putthe same in service. Replacement of the fusible element 88 may' beeasily and quickly made by unscrewing the casing 2 from the terminal cap6, whereupon the casing 2 may be replaced by another casing, or may bereadily manipulated to attach one terminal of a replacement fusibleelement 88 to the conductor 88 and the other terminal thereof to theconducting strip 98. Thereafter the casing may be threaded. into theterminal cap 6 and the break contact tongue I moved into engagement withthe contact tongue ii to thereby place our interrupter in condition forservice.

It is believed obvious from the foregoing that we have provided a novel,compact and relatively simplified form of automatic reclosing circuitbreaker, adapted to be mounted disconnectingly with respect to anassociated circuit, and further successive reclosures thereof to loci:the contacts of the interrupter open in the event an excessive number ofreclosures is attempted, together with relatively simple means ,wherebythe interrupter may again be placed in serviceable condition following alookout operation. It will be noted, furthermore, that the automaticoperation of both opening and reclosing the interrupter contacts, and oflocking the contacts in a closed position is controlled by a singlecontrol member, namely. the bimetal strip 82. The bimetal strip iscapable of occupying three operative positions in one of which, as'shownin Fig. 1, it controls and in another of which, as shown in Fig. 2, itcooperates with a latching means to lock the contacts closed, and in athird position (not shown) to the left of that shown in Fig. 2 itoperates to release the latch holding the contacts closed and therebypermit them to be opened. This single control member also operates witha time lag, since it depends for its movement to the positions statedabove upon the time required to heat the strip 82 which will be arelatively long time on light overloads and correspondingly shortertimes on heavier overloads.

Having described a preferred embodiment of our invention in accordancewith the patent statutes, we desire that our invention be interpreted asbroadly as possible inasmuch as it will be obvious, particularly topersons skilled in the art, that many changes may be made in theparticular structure disclosed without departing from the broad spiritand scope of our invention. Therefore, we desire that the followingclaims be interpreted as broadly as possible and that they be limitedonly by the prior art and by what is expressly stated therein.

We claim as our invention:

1. In a circuit interrupter including at least one pair of separablecontacts, means biasing at least one of said contacts away from theother of said contacts, latch means for maintaining said contacts intheir closed position electro-responsive means for releasing said latchmeans in response to passage through the interrupter of currents above apredetermined value to permit said contacts to separate, and meanscontrolled by 85 said electro-responsive means for closing saidenergization of the contact closing means 82,

contacts in their closed position, electro-responleasing operation, saidelectro-responsive means including a movable control element movable tothree different operative positions, including, respectively, a normalposition at which said contacts are latched closed, a .latch releasingpositlon, and a position for actuating said contact closing means.

2. In a circuit interrupter including at least one pair of separablecontacts, means biasing at least one of said contacts away from theother of said contacts, latch means for maintaining said contacts intheir closed position, electrorespons ve means for releasing said latchmeans in response to passage through the interrupter of currents above apredetermined value to permit said contacts to separate, meanscontrolled by said electro-responsive means for closing said contacts apredetermined time after a latch releasing operation, saidelectro-responsive means including a movable control element movable tothree different operative positions, including, respectively, a normalposition at which said contacts are latched closed, a latch releasingposition, and a position for actuating said contact closing means, andsaid electro-responsive means being constructed and arranged in a mannersuch that said control element is relatively slowly moved to itsaforesaid positions.

3. In a circuit interrupter including at least one pair of separablecontacts, means biasing at least one of said contacts away from theother of said contacts, latch means for maintaining said contacts intheir closed position, electro-responsive means for releasing said latchmeans in response to passage through the interrupter of curcontacts apredetermined time after a latch releasing operation, saidelectro-responsive means including a movable element normally biased toa position in which it energizes said contact closing means, saidelement being positioned at said normal position to be engaged by saidlatch means in its latching movement to be moved thereby to a secondposition wherein said contacts are latched closed and said contactclosing means is deenergized, and said element being movable to a thirdposition in response to said currents above a predetermined magnitude torelease said latch means.

4. In a circuit interrupter including at least one pair of separablecontacts, means biasing at least one of said contacts away from theother of said contacts, latch means for maintaining said contacts intheir closed position, electroresponsive means for releasing said latchmeans in response to passage through the interrupter of currents above apredetermined value to permit said contacts to separate, meanscontrolled by said electro-responsive means for closing said contacts apredetermined time after a latch releasing operation, saidelectro-responsive means including a bimetal element connected in thecircuit through said interrupter and having a. movable portion whichnormally occupies a position for energizing said contact closing means,said portion in its normal position being engageable by a part of saidlatch means inits movement one pair of separable contacts, means biasingat least one' of said contacts away from the other of said contacts,latch means for maintaining said contacts in their closed position,electroresponsive means for releasing said latch means in response topassage through the interrupter of currents above a predetermined valueto permit said contacts to separate, electrically operated meanscontrolled by said electro-responsive means for closing said contacts apredetermined time after a latch releasing operation, and means incircuit with said electro-responsive contact closing means forinterrupting the circuit therethroush in response to a predeterminednumber of successive contact closing operations thereof.

8. In a circuit interrupter including at least one pair of separablecontacts, means biasing at least one of said contacts away from theother of said contacts, latch means for maintaining said contacts intheir closed position, electroresponsive means for releasing said latchmeans in response to passage through the interrupter of currents above apredetermined value to permit said contacts to separate, andelectrically operated means controlled by said electro-responsive meansfor closing said contacts a predetermined time after a latch releasingoperation, and fusible means-in circuit with said electro-responsivecontact closing means for interrupting the to latched position so as tobe moved thereby to i a second or latching position, and said portionbeing movable in response to said-currents above a predeterminedmagnitude to a third position for releasing said latch means.

5. In a circuit interrupter, contact means mounted for movement into andout of engagement with respect to cooperating contact means, meansbiasing said contact means away from said cooperating contact means,contact closing means operable when energized to move said contact meansinto engagement with said cooperating contact, movable latch meansassociated with adapted to occupy a position for energizing said contactclosing means.

6. In a circuit interrupter, contact means mounted for movement into andout of engagement with respect to cooperatingcontact means, meansbiasing said contact means away from said cooperating contact means,contact closing means operable when energized to move said contact meansinto engagement with said cooperating contact, movable latch meansassociated with said movable contact means and normally biased tocooperate with a bimetallic element for latching said contact means inengagement, said bimetallic element being electrically connected in thecircuit through said interrupter so as to move in response to thepassage of currents th'erethrough above a predetermined value toreleasesaid movable latch means, said bimetallic element normallyadapted Q to occupy a position for energizing said contact closingmeans, and said movable latch means in its movement to latched positionbeing positioned to engage said bimetallic element and move the samefrom its said last mentioned position.

7. In a circuit interrupter, including at least circuit therethrough inresponse to a predetermined number of successive contact, closingoperations thereof. 1

9. In a circuit interrupter including at leut one pair of separablecontacts, means biasing at least' one of said contacts away from theother of said contacts, latch means for maintaining said contacts intheir closed-position, electroresponsive means for releasing said latchmeans in responseto passage through the interrupter of currents above'apredetermined value to permit said contacts to separate, solenoid meansthe energization of which is controlled by said electro-responsive meansfor closing said contacts a predetermined time after a latch releasingoperation, and fusible means in circuit with said "solenoid means andthe characteristics of which are such that it will fuse to open thesolenoid means circuit to render said solenoid means inoperative after apredetermined number of successiveenergizations thereof.

10. In a circuit interrupting device, a substantially closed containerhaving a pair of termi nals, interrupting means in said containerincluding relatively fixed and movable contacts connected to saidterminals, respectively, control means automatically controlling themovement or said movable contact into and out of engagement with'respectto said relatively fixed contact, said moving contact being actuated inone direction of movement by electrical means controlled by said controlmeans, and circuit interrupting means in circuit with said electricalmeans for interrupting the circuit and rendering said electrical meansinoperative after a predetermined number of successive energizationsthereof.

11. In a circuit interrupting device, a substantially closed containeradapted to contain an arc extinguishing liquid and having a pair ofterminals, interrupting means in said container including relativelyfixed and movable contacts one direction of movement by electrical meanscontrolled by said bimetallic means. and current responsive thermalcircuit interruptina means in circuit with said electrical means forinterruptin: the circuit and rendering said electrical means inoperativeafter a predetermined number of successive energizations thereof, saidcontacts, bimetallic means and current responsive thermal interruptingmeans positioned to be below the level of said liquid.

12. In a circuit interrupter, including at least one pair or separablecontacts, means biasing at least one of said contacts away from theother 01 said contacts, latch means for maintaining. said contacts intheir closed position, motive HERBERT L. RAWLINS. JAMES M. WALLACE.

